The present invention relates to an antenna device for emitting a radio identification signal, to a radio identification system and to a method for emitting a radio signal, like a radio identification or radio frequency identification (RFID) signal. In addition, the present invention relates to an RFID antenna including autonomous beam shaping.
In logistics, radio-frequency transponders or radio frequency identification (RFID) transponders which allow objects to be identified are more frequently used. Typically, these transponders are passive, but they may also be active. The transponders are excited by a radio-frequency electromagnetic field. The transponder makes use of this signal and transmits a modulated signal back to the reading station as a response to exciting. Information of the transponder which can be evaluated by the reading station are contained in the response signal. Thus, an object may be identified and associated unambiguously using a transponder.
Logistics processes, like identifying objects on a pallet, can be handled and optimized using this radio-frequency identification of objects. When a very large number of objects including transponders are located on a pallet, all the transponders can be read out and, consequently, all the objects can be identified within a certain time by a specific reading process. This allows an automatic detection of objects.
Today's systems, as used when passing gates or in displacing units, include a reading unit having one to four terminals to which a respective antenna may be connected. The radio-frequency excitation signal is emitted via the antenna(s) and the response signals of the transponders are received. With reading stations having a single terminal, single antennas have typically been used so far (1 gate−1 single antenna). Reliable detection of a large number of tags (transponders) here means longer a detection duration than when using several antennas, since a large number of collisions between the response signals may result and spatial filtering is not possible. In addition, the detection region (so-called visual or reading range) is considerably smaller compared to using several antennas and the respective gate number of readers and/or the number of readers. With regard to reading units having several gates, one gate each is connected to an antenna. When reading many transponders, the antennas within the reading unit are switched sequentially. This allows achieving a higher reading rate of transponders, which corresponds to a reduced detection duration. Increasing the reading rate, however, is dependent on the arrangement of the antennas. In order to make use of spatial filtering, the antennas are to be arranged in the most distributed manner possible so that the directional patterns thereof correlate only slightly and, thus, complementary space regions may be covered. The distributed arrangement here causes high space requirements.
Apart from distributing several antennas, spatial filtering may alternatively be realized by a feed network, for example by a Butler matrix, as is described in [1]. FIG. 11a shows an exemplarily total set up of a multi-beam antenna. FIG. 11b shows a realization of a feed network including a Butler matrix. Depending on which input gate of the network the excitation signal is applied to, a directional pattern oriented in a certain spatial direction will form. The feed network here distributes the input signal over all the antennas available connected at the output. The directional pattern of the antenna may thus be shaped by the respective phase and amplitude occupancy caused by the feed network. This type of antenna is called multi-beam antenna. In order to be able to make use of this type of spatial filtering with existing solutions, reading units having several antenna terminals are to be used, which cause considerably higher costs than apparatuses having a single antenna terminal.
With known solutions, switching between the single beams takes place by means of an interface, that is an external device, typically sensors for position identification of the pallet+external interface, determines the beam manifestation.
In further known systems, a number of antennas which are driven via specially configured reading systems are distributed over a total cover region. However, this is not a multi-beam system. Using standard reading units is not possible here so that the result is increased costs as regards complexity of the reading units and the distributed arrangement of the antennas.
Further known solutions offer a multi-beam solution including beam shaping. A high number of antenna beams which are simply connected to be active one after the other can be generated, however, the antennas are implemented to be so-called “leaky wave” antennas and limited strongly in their frequency domain. In addition, the directional pattern of the single antenna changes with a changing drive frequency so that the operating range of the device is limited.
Consequently, a concept would be desirable using which an efficient identification of radio identification transponders, which may be realized with little additional complexity relative to existing readers, can be obtained.
An object of the present invention is providing an antenna device which increases an identification rate and the visual or reading range of existing radio identification reading units with only little modification complexity compared to known antenna systems.
Another object of the present invention is providing a concept which allows increasing a rate of information relative to the detected radio identification transponders detected by a radio identification reader.